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Hello all, I am new to this forum and hoping I can get some help. I have a 1995 k2500 suburban 4x4 with the stock 6.5 gm diesel out of a 1998. It has approx. 140k on it. My issue is I cannot keep it from overheating when I am towing my camper. Which fully loaded with gear and all that good stuff is probably about 7500lb give or take. It's mainly bad when I start hitting some hills, and it doesn't take that big of a hill either. Currently modifications are: 4" exhaust, heath diesel tow /haul prom chip, cold air intake, adjustable mechanical wastegate controller,and PMD relocate ,it also has the dual thermostat set up and I am using the original type gm oem stats, Egt gauge,boost gauge and mechanical water temp gauge. I have also installed a brand new oem type radiator and condenser, the 2000+ 251-603 "new and improved water pump" , Hayden 2886 clutch fan, and the duramax fan blade. It still overheats upwards of 225deg. on a warm summer day in Buffalo,NY when pulling my trailer running up hills. I even turn off the A/C which helps a little but not much. Also, the head gaskets have been replaced and the external engine oil cooler is brand new. I am out of ideas and very frustrated at this point. Note: I am a mechanic have been for 30 years so this is now a mission for me to find and correct !!! Looking for any help...Thank You !!!
 

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Welcome to DieselPlace
Did you install the correct Radiator for the 6.5L? Where did you source the radiator?
Which T stats did you install? AC/Delco 180*/190* or 195*??
 
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Thanks for replying ! I sourced the rad locally through my local parts supplier, it was identical to the oem one as far as tube rows and size, other than original was copper brass and new one is aluminum with plastic tanks, also I really don't think there were any issues with the old one, I am using ac delco 131-103 t-stats that i purchased right from GM.I believe they are 192 deg. stats. I have also tried 180deg. and 195 deg. stats with really know difference in the overheating issue.
 

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First thing, wash the cooling stack.
This is in front of the truck behind the grill where the radiator, condenser and coolers are located.
Wash that thoroughly.

I hope you did this when you replace the radiator.
 
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Yes I did , I actually have washed it numerous times, probably like once a month or so.
 
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Thanks for replying ! I sourced the rad locally through my local parts supplier, it was identical to the oem one as far as tube rows and size, other than original was copper brass and new one is aluminum with plastic tanks, also I really don't think there were any issues with the old one, I am using ac delco 131-103 t-stats that i purchased right from GM.I believe they are 192 deg. stats. I have also tried 180deg. and 195 deg. stats with really know difference in the overheating issue.
You might try a different fan clutch

The Hayden clutches we list for the cooling mods are: 6.5 Cooling system Parts and pieces for upgrade
4 bolt fan clutch - Hayden severe duty:# 2839 (stock engagement)
Spin on fan clutch - Hayden Severe Duty spin on Fan clutch: #2840 (stock engagement)
I listed both options for whichever application you have.

The Hayden 2886 that you installed might be the wrong one for the job :unsure:
 

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ok, I will double check the number I believe I still have the box. But I do have the spin on type .thanks
 

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Welcome. Do you have a flow restricting fitting at the bypass hose?
I found it helps to keep the engine revs up when climbing thru the mountains.
 

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No, I do not but have considered installing one,however the cheapest I found was $79 ! thats nuts. I think I will try and make one for that kind of money.
 
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No, I do not but have considered installing one,however the cheapest I found was $79 ! thats nuts. I think I will try and make one for that kind of money.
The BRF ( bypass restrictor fitting) is important to have if you have the dual stats. It helps even the cooling flows over the heads to prevent any possible steam pockets from forming which can eventually crack your heads and tends to cook the #7 & #8 cylinders
 
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well I certainly wish I would have heard about this bypass fitting a long time ago all the reading and research that I have done Nova where do I recall them mentioning anything about this bypass fitting. Call me cheap but I just have a problem bringing myself to spend $80 for a $5 fitting so I made my own got to clean it up a little yet, and not the prettiest looking thing but looks like it should work. Thoughts..?
635232
635233
 

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well I certainly wish I would have heard about this bypass fitting a long time ago all the reading and research that I have done Nova where do I recall them mentioning anything about this bypass fitting. Call me cheap but I just have a problem bringing myself to spend $80 for a $5 fitting so I made my own got to clean it up a little yet, and not the prettiest looking thing but looks like it should work. Thoughts..? View attachment 635232 View attachment 635233

That looks like it should do the trick

(y)
 
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well I certainly wish I would have heard about this bypass fitting a long time ago all the reading and research that I have done Nova where do I recall them mentioning anything about this bypass fitting. Call me cheap but I just have a problem bringing myself to spend $80 for a $5 fitting so I made my own got to clean it up a little yet, and not the prettiest looking thing but looks like it should work. Thoughts..? View attachment 635232 View attachment 635233
This is great! I have all the same upgrades done to my 98 but still heats, going to make one of those restrictors asap.
 
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This is great! I have all the same upgrades done to my 98 but still heats, going to make one of those restrictors asap.
Welcome to DieselPlace
Be sure to fill out your signature with vehicle info ( Year, Make and Model) and list any known mods.

(y)
 
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Discussion Starter #15
I should have a pretty good idea of whether or not this is going to make a difference after next weekend , going camping will be Towing my trailer and hitting some pretty good-sized Hills. I have no idea what size the hole is on the aftermarket bypass fittings that a couple of places are selling for anywhere from $79 to $99 I did my best to guesstimate just looking at pictures and I ended up using a couple of washers and Welding them in place on my stock fitting which started out with a ID of .750 the washers I ended up using had an ID of .430
 

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It should roughly equal out to be a 3/8" hole and it will work fine
 

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Discussion Starter #17
(y)
 

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Have you considered your ratio of coolant to water? I know it seems a bit simple. But I’m a fan of KISS. Lol. The higher the concentration of antifreeze, the less heat it will pull and release from the radiator. Also a think to consider when swapping fans are the cfms they pull. I have a stock lb7 fan and that thing pulls 10k cfms. Maybe the setup you have isn’t pulling enough air thru the radiator? I have heard that the 6.5 did have an issue with getting hot.
 

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I installed the bypass restriction on my 6.5 and it fixed my heating issues, i used a 3/8 washer and welded it on, similar to headknocker95's picture.
I think this little guy should be advertised more. seems like it would be a good first upgrade, and cheep too!
 

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I should have a pretty good idea of whether or not this is going to make a difference after next weekend , going camping will be Towing my trailer and hitting some pretty good-sized Hills. I have no idea what size the hole is on the aftermarket bypass fittings that a couple of places are selling for anywhere from $79 to $99 I did my best to guesstimate no just looking at pictures and I ended up using a couple of washers and Welding them in place on my stock fitting which started out with a ID of .750 the washers I ended up using had an ID of .430
The hole in the store bought restrictor fitting is 3/4”. I measured mine before the install , a curiosity thing I suppose. 😹😹😹
 
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